1. Field of the Invention
The present invention relates to a process and a device for bonding two millimeter elements. Millimeter elements are implemented with signals whose frequency is typically greater than 30 GHz.
It makes it possible in particular to bond two millimeter elements consisting of a millimeter circuit made on a printed circuit implementing conducting lines of the microstrip type.
2. Discussion of the Background
Printed circuits on which millimeter circuits are made contain propagation lines which are mainly of two types.
The first type is said to be coplanar. In this case, the printed circuit implements coplanar lines. A coplanar line consists of a conducting line surrounded by two earth planes situated symmetrically on either side of the conducting line; the conducting line and the earth planes being situated on the same face of the substrate of the printed circuit. The bonds between millimeter circuits are made by wires. These bonds can introduce disturbances when the circuits to be bonded are too far apart. This is because an electric field spreads horizontally between the central conductor, connected to the conducting line, and the lateral conductors, situated on either side, connected to the earth planes. The characteristic impedance of this propagation line is determined mainly by the ratio between the width of the conductor and the width of the space between the central conductor and the lateral conductors, as well as by the dielectric constant of the support, namely air.
The second type is the so-called microstrip. In this case, the printed circuit implements microstrip lines. The printed circuit thus comprises a dielectric substrate with two main faces, an upper and a lower. A conductor having the form of a strip is made on the upper face and an earth conductor is made on the whole of the lower face. In accordance with this arrangement an electric field spreads between the strip-like conductor and the earth conductor. When making a microwave-frequency device, various millimeter elements are arranged in a specific metal casing. The millimeter elements may consist of millimeter circuits made on a printed circuit, of substrates or of components. Each millimeter element is attached to a bedplate screwed onto the metal casing. Under these conditions, earth continuity is achieved on the one hand by soldering or by conductive cementing to the entire surface of the printed circuit and on the other hand by screwing the bedplate to the metal package. In the millimeter frequency region, the earth continuity of the microwave-frequency device described above may not be of sufficient quality. In particular, when earth continuity is ensured by contact, between a package screwed onto the casing and the casing for example, the latter may not be of good quality, if the screwing is insufficient or if the surfaces in contact are not perfectly plane, for example. Moreover, when two millimeter circuits to be bonded are far apart, the techniques described above may not be useable.